The Borderlands games are ridiculous over the top and tremendous fun in co-op, so you really should be playing them.
And now there's even less reason not to get involved, with massive discounts on the PC version of the game over at Funstockdigital. Check out the deals.
Borderlands GOTY - 75% off
Borderland 2 - 75% off
Borderlands 2 GOTY - 48% off
Borderlands: The Pre-Sequel - 47% off
It seems like you have to use the code#FUNISHOT when checking out to get the full discount, so make sure to do that. And get Borderlanding!